In the Long-Term Evolution (LTE) mobile communication system defined by the 3rd Generation Partnership Project (3GPP), uplink radio transmissions utilize Discrete Fourier Transform (DFT)-spread-OFDM (DFTS-OFDM) techniques. FIG. 1a is a block diagram illustrating how DFTS-OFDM works. Blocks of M modulation symbols 101 are first applied to a size M DFT 103. The output of the DFT 103 is then supplied to a frequency mapper 105, which maps the DFT output to selective consecutive inputs of a size N Inverse DFT 107 that can, for example, be implemented by means of Inverse Fast Fourier Transform (IFFT) processing. By adjusting the block size M, the instantaneous bandwidth of the transmitted signal can be varied. Similarly, by adjusting (e.g., shifting) the set of IFFT inputs to which the DFT output block of size M is mapped, the frequency-domain position of the transmitted signal can be adjusted. DFTS-OFDM can be thought of as an OFDM transmission (an IFFT) preceded by a DFT-based pre-coding. Thus, as with OFDM, the spectrum of a DFTS-OFDM signal can be seen as consisting of a number of subcarriers.
In some other mobile communication standards, pure OFDM is used instead of DFTS-OFDM. FIG. 1b is a block diagram illustrating how pure OFDM works. Blocks of M modulation symbols 111 are applied directly to a frequency mapper 113, which maps the M modulation symbols to selective consecutive inputs of a size N Inverse DFT 115 that can, for example, be implemented by means of Inverse IFFT processing. By adjusting the block size M, the instantaneous bandwidth of the transmitted signal can be varied. Similarly, by adjusting (e.g., shifting) the set of IFFT inputs to which the DFT output block of size M is mapped, the frequency-domain position of the transmitted signal can be adjusted. As mentioned above, the spectrum of an OFDM signal can be seen as consisting of a number of subcarriers.